This proposal builds on the established library of monoclonal antibodies to Drosophila nuclear protein and the recently developed tools of three-dimensional reconstruction of subcellular structures. This proposal focusses on a subset of the antibodies that label the nuclear envelope. Using electron microscopy, the substructure and location within the nuclear envelope will be established. Further correlation of the nuclear envelope substructures to the interphase chromosomes by the three-dimensional image processing techniques will be accomplished. The antigen will be purified and extensively characterized by biochemical procedures.